Effluent Total Nitrogen Research Articles

Technical Performance and Environmental Effects of the Treated Effluent of Wastewater Treatment Plants in the Shenzhen Bay Catchment, China

Technical performance and effluent environmental impact of seven wastewater treatment plant (WWTPs) in the Shenzhen Bay Catchment, China were examined. All WWTPs had good performance in the removal of chemical oxygen demand, biochemical oxygen demand, and suspended solids, while total nitrogen and total phosphorus removal should be enhanced to improve the comprehensive pollutants removal loading rate. The effluent eutrophication effect from WWTPs was in the range of 0.0028–0.0092 kg/m3, and nitrate was the major contributor. The effluent greenhouse gas emission of WWTP1–7 was in the range of 3.23 × 10−5–8.70 × 10−5 kg·CO2/m3. The effluent eutrophication effects and greenhouse gas emission of WWTPs could be reduced by decreasing the effluent total nitrogen concentration. The ecological risk and healthy risk of heavy metals were low. Among examined heavy metals, lead contributed the most to the ecological risk while arsenic contributed most to the human health risk. The human health risk of microbial pollutants of WWTPs1–7 was in the range of 0.0024–0.0042 DALY (Disability Adjusted Life Years). Finally, an ecosystem-based WWTP framework was proposed to systematically include all environmental effects so as to support the sustainable development of WWTPs.

Uncoupling the solids retention times of flocs and granules in mainstream deammonification: A screen as effective out-selection tool for nitrite oxidizing bacteria

This study focused on a physical separator in the form of a screen to out-select nitrite oxidizing bacteria (NOB) for mainstream sewage treatment. This separation relied on the principle that the NOB prefer to grow in flocs, while anammox bacteria (AnAOB) reside in granules. Two types of screens (vacuum and vibrating) were tested for separating these fractions. The vibrating screen was preferred due to more moderate normal forces and additional tangential forces, better balancing retention efficiency of AnAOB granules (41% of the AnAOB activity) and washout of NOB (92% activity washout). This operation resulted in increased NOB out-selection (AerAOB/NOB ratio of 2.3) and a total nitrogen removal efficiency of 70% at influent COD/N ratio of 1.4. An effluent total nitrogen concentration <10mgN/L was achieved using this novel approach combining biological selection with physical separation, opening up the path towards energy positive sewage treatment.

Nitrogen Removal of Municipal Wastewater by ANAMMOX Coupled Shortcut Nitrification in Anaerobic Baffled Reactor

If the technology of anaerobic ammonium oxidation(ANAMMOX) can substitute the mainstream technology of municipal wastewater treatment plant, the energy of municipal wastewater treatment will be decreased significantly. Thus, anaerobic baffled reactor(ABR) was used to build carbon system, shortcut nitrification system and anaerobic ammonia oxidation system. And the three systems were coupled to shortcut nitrification-anaerobic ammonia oxidation reactor to treat municipal wastewater. The results showed that the average effluent COD concentration of carbon removal system was 80 mg·L-1 when the hydraulic retention time of carbon removal system was 4.5 h. And the subsequent shortcut nitrification system would not be adversely affected by the effluent COD. Finally, the average effluent total nitrogen concentration was 10 mg·L-1, with total nitrogen volume load of ANAMMOX system of 0.36 kg·(m3·d)-1. When the dissolved oxygen was controlled between 1 to 2 mg·L-1, the nitrite accumulation rate could be maintained around 90%, ensuring the stable operation of the subsequent anaerobic ammonia oxidation system. The nitrogen of municipal wastewater could be stable and efficiently removed by the shortcut nitrification -ANAMMOX integration ABR with temperature of 30℃ and dissolved oxygen of 1-2 mg·L-1.

Effect of Biofilm Density on Nitrous Oxide Emissions and Treatment Efficiency on Sequencing Batch Biofilm Reactor

The reduction of nitrous oxide (N2O) emission during nitrogen removal process in municipal wastewater treatment is of great urgency. Sequencing batch biofilm reactor (SBBR) system could be a promising and efficient way to solve the problem. In order to get the high chemical oxygen demand (COD) and nitrogen removal efficiency and low nitrous oxide emission, the influence of biofilm density on SBBR was investigated. When the biofilm density changed from 15 to 30 %, the effluent COD, total nitrogen (TN) and ammonia nitrogen decreased, but the effluent TN concentration did not meet the class I-B standard of the Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant in China. COD, TN, and ammonia nitrogen concentration was 42.34, 19.14 and 2.97 mg/L at 50 % biofilm density. When the density turned from 50 to 70 %, although the effluent COD, TN, and ammonia nitrogen were still decreased, N2O emission increased from 0.45 to 0.77 %. Considering the effluent quality and N2O emission, the optimal biofilm density in SBBR was 50 %.

Pilot-Scale Study of an Integrated Membrane-Aerated Biofilm Reactor System on Urban River Remediation

Coupled with the hydrolysis–acidification (H–A) process, the two-stage continuous flow membrane-aerated biofilm reactor (MABR) system was designed for urban river treatment, and parameter optimization was investigated in accordance with the average effluent concentrations of chemical oxygen demand (COD), ammonia nitrogen (NH4+–N), total nitrogen (TN), and suspended solids (SS). The optimal process parameters included temperature, 19 °C; pH, 8.0; the reflux ratio, 200%; and hydraulic retention time (HRT), 15 h, based on which the operational feasibility of the integrated system was further evaluated during the 40 days pilot-study for the urban river treatment. Results indicated that the integrated system exhibited highly effective performance for the urban river remediation with ∼87% COD removed and >95% NH4+–N removed. Nitrification and denitrification were simultaneously achieved inside the system. The TN removal process was enhanced by the reflux system with the effluent TN concentration remaining at ∼1...

Driving forces of effluent nutrient variability in field scale bioretention

Nutrient exports from urbanized watersheds have been identified as a major contributor to surface water degradation worldwide. As efforts to implement stormwater treatment controls, such as bioretention, become increasingly common, understanding how the functionality of these systems varies based on environmental conditions is critical. Quantifying this variability and its causes will aid in developing more robust models and watershed restoration plans which incorporate the uncertainty of bioretention function. This study investigated effluent nutrient concentrations from ten bioretention areas in North Carolina, USA. Nitrogen species were found to have higher variability than phosphorus species, with changes in effluent concentrations being significantly influenced by environmental conditions. In particular, effluent concentrations of total nitrogen (TN) and nitrate (NO3-N) were strongly correlated to antecedent rainfall depth and temperature. As antecedent rainfall depth increased, NO3-N and TN concentrations decreased. These trends have been noted in other laboratory-based studies and are logical based on the influence of dry conditions on microbial communities. Increases in ambient temperature were shown to increase effluent TN and NO3-N concentrations in conventionally drained systems. However, a negative correlation was found between temperature and effluent NO3-N concentrations in systems with an internal water storage (IWS) layer, suggesting increased denitrifying microbe activity. These results show that variability in effluent nutrient concentrations can be explained by environmental conditions, and that the effects of these conditions may differ based on system design.

Performance of constructed wetland applied for domestic wastewater treatment: Case study at Boimorto (Galicia, Spain)

The study aims at evaluating the performance of a horizontal subsurface flow constructed wetland used for secondary treatment of domestic wastewater since May 2011 at Galicia (Spain). A septic tank was used as primary treatment. The wetland consists of two cells in parallel: cell-A with 350m2 and cell-B with 280m2, constructed with a depth of 0.6m, filled with gravel of 30mm of average size and planted with common reeds. The performance of wastewater treatment was controlled from June 2011 to September 2015. The rural agglomeration is served by a gravity sewer system with high rates of infiltration/inflow during wet weather. Thus, concentration and flow rate of wastewater have high seasonal variability. Average primary effluent BOD5, COD, suspended solids (TSS), total nitrogen (TN) and total phosphorous (TP) concentrations (in mg/L) were: 105, 197, 43, 29 and 3.4, respectively. Meanwhile, average secondary effluent BOD5, COD, SS, TN and TP values (in mg/L) were: 19, 44, 12, 14.3 and 1.9, respectively. A 2.2 log unit reduction for faecal coliforms was observed in the global system. The wetland required to be harvested at the end of each October. The sludge produced by the septic tank has not yet required to be removed. The wetland system presented no problems for vectors or nuisance odours.

Advanced nitrogen removal from landfill leachate via Anammox system based on Sequencing Biofilm Batch Reactor (SBBR): Effective protection of biofilm

High levels of organics negatively affect Anammox for treating landfill leachate. To enhance the ability of Anammox to survive against adverse environments, a lab-scale two-stage Anammox system using a Sequencing Biofilm Batch Reactor was applied to treat mature landfill leachate under 35°C. Over 107days, with influent total nitrogen (TN) and chemical oxygen demand (COD) concentrations of 3000±100 and 3000±100mg/L, effluent TN was below 20mg/L. For extracellular polymeric substance (EPS) of Anammox, slime-EPS and loosely-bound-EPS of floccules were both higher than biofilm, while tight-bound-EPS of biofilm was significantly higher, contributing to biofilm formation. Quantitative microbial analysis showed that as influent COD increased, Anammox gene ratios of biofilm increased from 1.34% to 13.28%; the gene ratios of floccule first increased, then decreased to 3.88%. This indicated that Anammox and heterotrophic bacteria could coexist because of the biofilm, leading to stable nitrogen removal performance, even when organics were present.

Feasibility of enhancing the DEnitrifying AMmonium OXidation (DEAMOX) process for nitrogen removal by seeding partial denitrification sludge

The recently proposed DEnitrifying AMmonium OXidation (DEAMOX) process combined anaerobic ammonia oxidation (ANAMMOX) with denitrification to convert nitrate to nitrite, which was a promising way for treating wastewater containing nitrate and ammonia. This study investigated the feasibility of establishing DEAMOX process by seeding partial denitrification sludge (NO3− → NO2−) using sodium acetate as an electron donor in a sequencing batch reactor. Results showed that the DEAMOX process was established successfully and operated stably in 114-days operation. The average effluent total nitrogen concentration was below 5 mg L−1 and TN removal efficiency reached up to 97% at COD/NO3− ratio of 3.0 under initial NH4+ concentration of 25 mg L−1 and NO3− of 30 mg L−1. It suggested that the presence of NO2− in the system supplied for ANAMMOX and the relatively long sludge retention time (SRT) for denitrifiers were attributed to commendable coexistence of ANAMMOX and denitrifying bacteria.

Modeling organic matter and nitrogen removal from domestic wastewater in a pilot-scale vertical subsurface flow constructed wetland

ABSTRACTConstructed wetlands have become an attractive alternative for wastewater treatment. However, there is not a globally accepted mathematical model to predict their performance. In this study, the VS2DTI software was used to predict the effluent biochemical oxygen demand (BOD) and total nitrogen (TN) in a pilot-scale vertical flow constructed wetland (VFCW) treating domestic wastewater. After a 5-week adaptation period, the pilot system was monitored for another 6 weeks. Experiments were conducted at hydraulic retention times (HRTs) in the range of 2–4 days with Typha latifolia as the vegetation. The raw wastewater concentrations ranged between 144–430 and 122–283 mg L−1 for BOD5 and TN, respectively. A first-order kinetic model coupled with the advection/dispersion and Richards' equations was proposed to predict the removal rates of BOD5 and TN from domestic wastewater. Two main physical processes were modeled in this study, porous material water flow and solute transport through the different layers of the VFCW to simulate the constructed wetland (CW) conditions. The model was calibrated based on the BOD5 and TN degradation constants. The model indicated that most of BOD and TN (88 and 92%, respectively) were removed through biological activity followed by adsorption. It was also observed that the evapotranspiration was seen to have a smaller impact. An additional data series of effluent BOD and TN was used for model validation. The residual analysis of the calibrated model showed a relatively random pattern, indicating a decent fit. Thus, the VS2DTI was found to be a useful tool for CW simulation.

Evaluation of High Density Algal Cultivation for Secondary Wastewater Polishing.

This study evaluated the performance of an algal membrane bioreactor (A-MBR) for secondary wastewater effluent polishing and determined the membrane fouling behavior and dominance of algae in the A-MBR. The continuous flow A-MBR (effective volume = 7.2 L) was operated with low biomass wastage for more than 180 days, resulting in an average algal mixed liquor suspended solid concentration of 4922 mg/L. At the influent concentrations of 43 mg/L COD, 1.6 mg/L total phosphorus (TP), and 11.8 mg/L total nitrogen (TN), the effluent COD, TP and TN concentrations were 26 ± 6 mg/L, 0.7 ± 0.3 mg/L, and 9.6 ± 1.2 mg/L, respectively. High-density algae cultivation facilitated P adsorption and chemical precipitation. However, the TN removal efficiency was only 14% because of low biomass wastage. Although bacteria represented less than 2% of the total biomass in the A-MBR, bacterial growth in the secondary wastewater effluent accelerated membrane fouling.

Influence of Internal and External Recycle on Nitrogen Removal in Compact Bioreactor

Internal Recycle ratios (IR) were alternated and operated to determine its efficiency on nitrate removal within a SMALL FOOTPRINT bioreactor. Determining a suitable recycle ratio is essential to justify the prerequisites required for operative optimization. In order to achieve considerable nitrogen reduction, the reactor was designed with primary (pre) and secondary (post) anoxic chambers, combined aeration chamber for nitrification and carbon removal and final settler to settle the biomass prior to discharge. The nitrate oxidized in aeration chamber was recycled back to the pre-anoxic chamber. The residual nitrate flows to the post anoxic chamber for denitrification. Each IR ratio of 6, 4 and 0, was operated with distinct influent Chemical Oxygen Demand (COD) to Total Kjeldahl Nitrogen (TKN) ratios of 18.9, 14.9 and 10.9, respectively. The IR of 6 with COD/TKN ratio of 18.9 attained maximum Total Nitrogen (TN) removal efficiency of 90.7%. The overall average total nitrogen (TN) = 4.0 mg/L in effluent was achieved, signifying an average of 9.5% efficiency more than the process without nitrate recycle, with average effluent TN = 7.7 mg/L.

Simultaneous biological removal of nitrogen and phosphorus in a vertical bioreactor

Nutrients pollution has become a global environmental threat. A large fraction of nutrient pollution is caused by point sources like the discharges of untreated domestic and industrial wastewater. As a result, there is a great demand to develop reliable, compact and efficient nutrient removal technologies. In the wastewater industry, most of the bioreactors have a large foot print with a plane configuration. Furthermore, the existing nutrient removal processes are based on well-known microbial species of genus Nitrosomonas and Nitrobacter involved in nitrification/denitrification and Candidatus Accumulibater Phosphatis responsible for biological phosphorous removal (BPR). The present work is unprecedented in two aspects: (1) The biological nitrogen and phosphorus removal from wastewater occurred in a multistage vertical, tubular bioreactor and (2) Two abundant microbial species were responsible for the simultaneous nitrification–denitrification–BPR in this vertical bioreactor. The abundant microbial populations included an unidentified bacteria of Saprospiraceae family and bacteria affiliated with the genus Zoogloea. The composition of the synthetic wastewater used in this study was: total phosphorous (TP) 32.6±0.7mg/L, total nitrogen (TN) 272±7.5 in which 45±1.8mg/L was ammonia-nitrogen (NH3-N). The bioreactor was continuously operated for over 350 days at constant flowrate, temperature and pH of 240 (L/day), 22–24 (°C) and 7–7.5. The results showed that simultaneous nitrification–denitrification–BPR was the dominant process by an, as yet not fully classified, microbial species. The effluent TP and TN concentrations were 2.7±0.4 and 4.3±1.2mg/L respectively. Concentrations of NH3-N, NO2− and NO3-N in the effluent were 0.7±0.1, 0.8±0.5 and 0.3±0.1. The simultaneous nitrification–denitrification–BPR was highly effective delivering above 90% TN and TP removal efficiency. The successful results presented in this paper have led to the construction of a 20,000L/day demonstration plant in the City of Pickering, Ontario.

Suppressing Nitrite-oxidizing Bacteria Growth to Achieve Nitrogen Removal from Domestic Wastewater via Anammox Using Intermittent Aeration with Low Dissolved Oxygen.

Achieving nitrogen removal from domestic wastewater using anaerobic ammonium oxidation (anammox) has the potential to make wastewater treatment energy-neutral or even energy-positive. The challenge is to suppress the growth of nitrite-oxidizing bacteria (NOB). This study presents a promising method based on intermittent aeration with low dissolved oxygen to limit NOB growth, thereby providing an advantage to anammox bacteria to form a partnership with the ammonium-oxidizing bacteria (AOB). The results showed that NOB was successfully suppressed using that method, with the relative abundance of NOB maintained between 2.0–2.6%, based on Fluorescent in-situ Hybridization. Nitrogen could be effectively removed from domestic wastewater with anammox at a temperature above 20 °C, with an effluent total nitrogen (TN) concentration of 6.6 ± 2.7 mg/L, while the influent TN and soluble chemical oxygen demand were 62.6 ± 3.1 mg/L and 88.0 ± 8.1 mg/L, respectively.

Simultaneous Removal of Organic and Nitrogen in a Post-Denitrification Membrane Bioreactor (MBR) System and its Influential Factors

A post-denitrification membrane bioreactor (MBR) system was developed to simultaneously remove organics and nitrogen from domestic wastewater. From a long-term experimental investigation, more than 96% organics could be degraded biologically and the effluent Chemical Oxygen Demand (COD) was below 10.5 mg/L. With a Hydraulic Retention Time (HRT) of 13.6 h and a total recirculation ratio of 8×Q, the MBR system could obtain a stably high Total Nitrogen (TN) removal efficiency of up to 92.4%, resulted in an effluent TN content of as low as 2.80 mg/L. Effects of operating parameters, including HRT, Sludge Retention Time (SRT), recirculation ratio and influent C/N, onto the system treatment performance were evaluated. It was revealed that HRT and recirculation ratio had significant impacts onto TN removal efficiency, reflected by that a reduced HRT to 9 h and a lower recirculation of 6×Q induced to 78.2% TN removal and an effluent TN of about 14 mg/L. A proper SRT and C/N ranged from 12 to 40 days, and from 8:1 to 13.5:1, respectively, have insignificant impacts onto the organic degradation and ammonia-N removal. Nevertheless, TN removal was highly inhibited by low SRT and C/N ratios. MBR combination with post-denitrification helps to enhance the organic and nitrogen removal compared with conventional activated sludge process, as it ensured a high biomass level in the treatment system. Keywords: Biological nitrogen removal, membrane bioreactor (MBR), nitrogen gas, organic degradation, post-denitrification, wastewater treatment.

Effect of the mixing ratio during co-treatment of landfill leachate and sewage with a combined stripping and reversed A2/O process

In this study, pilot-scale tests were conducted to evaluate the effect of volumetric mixing ratio of landfill leachate to sewage on the performance of the combined ammonia stripping and reversed anaerobic/anoxic/oxic (A2/O) process for co-treatment of landfill leachate and municipal sewage. Stripping, as pre-treatment, could significantly remove ammonia nitrogen (NH3-N) and total nitrogen (TN) by 55% and 52%, respectively. Moreover, chemical oxygen demand (COD) was slightly reduced by 6.8%, and little total phosphorus (TP) was removed. The subsequent reversed A2/O process appeared to be highly influenced by the volumetric mixing ratio of leachate to sewage. Typically, the effluent COD, NH3-N, TN and TP increased with the increasing ratio from 1:30 to 1:15, namely, the increasing fraction of leachate. Over the all tested mixing ratio range, the effluent COD and NH3-N were satisfied with the primary B standards of Chinese Discharge Standard of Pollutants for municipal waste water treatment plant (GB18918-2002). The standards different from the primary A standards for water reuse are used for discharge into the most surface water bodies in China. However, TN and TP would exceed the primary B standard levels at a mixing ratio of 1:15 or greater. These findings suggest that an appropriate volumetric mixing ratio should be carefully selected to ensure the performance of the reversed A2/O process.

Nitrogen Removal Controlled by an Ammonium-Analyser at the north Pest Wastewater Treatment Plant

Abstract At the North Pest Wastewater Treatment Plant, a nutrient removal process has been in operation since 2011. New tanks have been built, which can receive approximately half of the pre-settled wastewater. A predenitrification system has been planned and built both to the old and new lines. Due to the relatively small anoxic zones, periodic aeration was initiated first in the new line to achieve the lowest possible effluent total nitrogen concentration. Because of its positive impact, the operation of periodic aeration was initiated in the old line as well. Ammonium-analysers are used to control the aeration periods. Due to this process, the plant can provide a very low total nitrogen effluent value (below 10 mg dm-3 on average) as well as save energy and operational costs.

Enhancing nitrogen and phosphorus removal in the BUCT-IFAS process by bypass flow strategy.

A University of Cape Town process coupled with integrated fixed biofilm and activated sludge system was modified by bypass flow strategy (BUCT-IFAS) to enhance nitrogen and phosphorus removal from the wastewater containing insufficient carbon source. This process was operated under different bypass flow ratios (λ were 0, 0.4, 0.5, 0.6 and 0.7, respectively) to investigate the effect of different operational modes on the nitrogen (N) and phosphorus (P) removal efficiency (λ=0 was noted as common mode, other λ were noted as bypass flow mode), and optimizing the N and P removal efficiency by altering the λ. Results showed that the best total nitrogen (TN) and total phosphorus (TP) removal performances were achieved at λ of 0.6, the effluent TN and TP averaged 14.0 and 0.4 mg/L meeting discharge standard (TN<15 mg/L, TP<0.5 mg/L). Correspondingly, the TN and TP removal efficiencies were 70% and 94%, respectively, which were 24 and 41% higher than those at λ of 0. In addition, the denitrification and anoxic P-uptake rates were increased by 23% and 23%, respectively, compared with those at λ of 0. These results demonstrated that the BUCT-IFAS process was an attractive method for enhancing nitrogen and phosphorus removal from wastewater containing insufficient carbon source.

Achieving low effluent NO3-N and TN concentrations in low influent chemical oxygen demand (COD) to total Kjeldahl nitrogen (TKN) ratio without using external carbon source

Two mathematical models were used to optimize the performance of a full-scale biological nutrient removal (BNR) activated treatment plant, a plug-flow bioreactors operated in a 3-stage phoredox process configuration, anaerobic anoxic oxic (A2/O). The ASM2d implemented on the platform of WEST2011 software and the BioWin activated sludge/anaerobic digestion (AS/AD) models were used in this study with the aim of consistently achieving the designed effluent criteria at a low operational cost. Four ASM2d parameters (the reduction factor for denitrification \((\eta _{NO_3 H} )\), the maximum growth rate of heterotrophs (µH), the rate constant for stored polyphosphates in PAOs (qpp), and the hydrolysis rate constant (kh)) were adjusted. Whereas three BioWin parameters (aerobic decay rate (bH), heterotrophic dissolved oxygen (DO) half saturation (KOA), and YP/acetic) were adjusted. Calibration of the two models was successful; both models have average relative deviations (ARD) less than 10% for all the output variables. Low effluent concentrations of nitrate nitrogen (N-NO3), total nitrogen (TN), and total phosphorus (TP) were achieved in a full-scale BNR treatment plant having low influent chemical oxygen demand (COD) to total Kjeldahl nitrogen (TKN) ratio (COD/TKN). The effluent total nitrogen and nitrate nitrogen concentrations were improved by 50% and energy consumption was reduced by approximately 25%, which was accomplished by converting the two-pass aerobic compartment of the plug-flow bioreactor to anoxic reactors and being operated in an alternating mode. Findings in this work are helpful in improving the operation of wastewater treatment plant while eliminating the cost of external carbon source and reducing energy consumption.

Modeling of effluent quality parameters in a submerged membrane bioreactor with simultaneous upward and downward aeration treating municipal wastewater using hybrid models

This research was an effort to develop hybrid multilayer perceptron and radial basis function artificial neural network–genetic algorithm (MLPANN-GA and RBFANN-GA) models to accurately predict effluent biochemical oxygen demand (BOD), chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) in a submerged membrane bioreactor. The input variables of the networks were influent BOD, influent COD, influent TN or influent TP, sludge retention time (SRT), mixed liquor suspended solid, membrane permeability, and transmembrane pressure. Training procedures of all effluent quality parameters were successful for both the MLPANN-GA and RBFANN-GA models. The training and testing models showed an almost perfect match between the experimental and predicted values. Based upon the statistical analysis, results indicated that there is a very little difference between predicted and experimental values of the effluent BOD, COD, TN, and TP. The predicted and experimental values of the effluent concentrations gave a very low root mean squared error and a high coefficient of determination very close to one demonstrated high accuracy of these models to predict output variables. It became clear that the models based on the genetic algorithm (GA) were much better than those models without GA from the viewpoint of the achievement of an accurate prediction of the effluent BOD, COD, TN, and TP. The results indicated that the accuracy of all models increased when GA was applied to neural networks. The mean average error for the hybrid models varied from 3 to 8%.